(Field of the Invention)
The present invention relates to an in-wheel motor drive device, and also relates to a technique for detecting an abnormality in the in-wheel motor drive device with high precision using a coil temperature sensor and an oil temperature sensor.
(Description of Related Art)
An in-wheel motor drive device includes a speed reducer, a motor, and a wheel bearing. A loss in the in-wheel motor drive device amounts to the sum of losses in those components of the in-wheel motor drive device. A loss in the speed reducer is mainly attributable to rolling resistance in a bearing section, and/or sliding resistance in a sliding portion. Given that bearing specifications and gaps inside the speed reducer are fixed, the magnitude of a loss due to such resistance depends on the rotation frequency (see FIG. 7).
In the motor, core losses, copper losses, and mechanical losses occupy a large part of a total loss. The magnitude of the copper losses depends on a coil electric current, the magnitude of the core losses depends on the coil electric current and the rotation frequency, and the magnitude of the mechanical losses depends on the rotation frequency. Therefore, the copper losses occupy a large part of the total loss in low-speed high-torque operation, while the core losses and the mechanical losses occupy a large part of the total loss in high-speed low-torque operation (see FIG. 8).
Accordingly, a loss map representing a total loss in an in-wheel motor drive device unit in accordance with the motor rotation frequency and motor torque as illustrated in FIG. 9 has an operation range A, which is occupied by losses attributable to the motor, and an operation range C, which is occupied by losses attributable to the motor and the speed reducer. An operation range B is where losses in the speed reducer and the motor are so small that abnormality detection does not need to be performed while the motor rotation frequency and the motor torque are fall within this range.
The total loss in the in-wheel motor drive device unit in the low-speed high-torque operation, which is represented by range A, is largely attributable to the copper losses in the motor. As a result, in the low-speed high-torque operation, an increase rate of the coil temperature is greater than an increase rate of the temperature of a lubricating oil, such that a change of temperature of the lubricating oil is greatly behind a change of coil temperature. Meanwhile, in the high-speed low-torque operation, which is represented by range C, the total loss in the in-wheel motor drive device unit is largely occupied by the core losses in the motor and the losses in the speed reducer, and the increase rate of the temperature of the lubricating oil is therefore greater than the increase rate of the coil temperature.
A coil temperature sensor is typically disposed between slots of a stator, and the lubricating oil therefore does not easily get on the coil temperature sensor, which makes it unlikely to directly measure the temperature of the lubricating oil with the coil temperature sensor. The temperatures of coils and the stator are increased by the lubricating oil getting on the coils and a stator core, and the coil temperature sensor responds to an increase in the coil temperature caused by conduction and transmission of the heat. An output of the coil temperature sensor therefore involves a significant delay in a response to the temperature of the lubricating oil.